Languages evolve to become easier (not harder!)
Let us begin with something we can all agree upon: languages change. In fact, only dead languages do not change. Now we can ask ourselves: "if languages change, wouldn't it be sensible to think that they change to become easier to learn?".
While the difficulty of a foreign language is to some extent relative, i.e. it depends on our first language, perhaps there are some absolute features that make a language inherently harder (e.g. noun genders, grammatical cases, verb conjugations, irregular verbs, a logographic writing system, etc.) and some others that make it easier (e.g. few and clear tenses, few declensions, exact correspondence of Orthography and Phonetics, clear syntax, consistent grammar rules with few or no exceptions, a writing system easy to learn, easy to read and easy to write, etc.)
Language evolution points towards easiness. Countless phrases that we take for granted today, would have been considered grammatically grotesque in previous centuries. Those 'mistakes' became the norm because they require less effort. Spanish, Portuguese, Italian and French are easy variants of Latin. Modern German is easier than Old High German and English is easier than German. When Turkish was written using a form of the Arabic script, the literacy rate was around 10%; when the latin script was adopted, literacy went over 90%. Considering Chinese, Japanese and Arabic, it becomes clear that when it comes to writing systems, the latin alphabet stands out as a formidable piece of technology.
Everything moves towards efficiency and effectiveness. Making a language harder would be like deciding to ditch our cars for horse carts. Can we conclude that the easier a language is, the more evolved it is?
Why am I starting this discussion? Because I am not a linguist, I can not overcome my biases and it is likely that this is a fallacious idea born out of ignorance.